Steel pin and method for its manufacture

ABSTRACT

A steel pin is disclosed of a type to be forcibly driven into a steel substrate by using a powder-actuated tool. The steel pin has a substantially cylindrical shank, and a substantially sharp point which extends from one end of the substantially cylindrical shank, which conforms substantially to a tangent or secant ogive except for a substantially spherical tip having a radius in the range of approximately 0.015 inch (approximately 3.75 millimeters) to approximately 0.03 inch (approximately 7.5 millimeters), which has substantially true concentricity, which has surface-texture irregularities with a roughness-height index value not greater than approximately 30 microinches (approximately 0.76 micrometers), and which appears to be substantially free of other surface imperfections when viewed under 60× magnification. Optimally, the ogive is a tangent ogive with an ogive radius approximately ten times the shank diameter and with an ogive length approximately twice the shank diameter, and the tip radius is approximately 0.1 times the shank diameter. The substantially cylindrical shank is joined to the substantially sharp point at a transition having a substantially smooth, continuously curved surface, and which is knurled near the transition. The steel pin is made by deforming a length of steel wire, as by forging or swaging, so as to form the steel pin.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division, of application Ser. No. 08/467,026,filed Jun. 6, 1995 now U.S. Pat. No. 5,658,109 which is in turn a CIP ofSer. No. 08/262,475 filed Jun. 20, 1994 now abandoned.

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/262,475, which was filed on Jun. 20, 1994, and thedisclosure of which is incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

This invention pertains to a steel pin of a type to be forcibly driventhrough a workpiece into a steel substrate by means of a powder-actuatedtool. The steel pin has a substantially sharp point, which is reshapedso that such point has substantially true concentricity, so thatsurface-texture irregularities on such point are reduced, and so thatsuch point appears under high magnification to be substantially free ofother surface imperfections. This invention also pertains to a methodfor the manufacture of the steel pin.

BACKGROUND OF THE INVENTION

Frequently, powder-actuated tools are employed to drive steel pins orfasteners through workpieces into steel, concrete, or masonrysubstrates. A powder-actuated tool employs a powder charge, whichundergoes explosive combustion.

High velocity tools, those without pistons, are no longer produced inthe industry. Current low velocity, powder-actuated tools drive thesteel pins or fasteners by means of a piston disposed between the chargeand the steel pin. These current low velocity tools result in a lowervelocity for the steel pin and thus lower energy imparted to the pin.Without proper design and manufacture of the steel pin or fastener,these tools may not have sufficient energy to drive a fastener deeplyenough into a steel substrate so as to provide adequate or consistentholding values to satisfy the needs of a specific application. Without aproperly designed pin, some would-be powder-actuated tool users may optfor other methods of holding articles to steel or concrete, substratessuch as inserting a fastener into a drilled hole.

Typically, such a pin is manufactured by drawing a steel wire to adesired diameter, cutting the drawn wire to a predetermined length whiledeforming one end of the length of wire so as to form a head, anddeforming the other end of the length of wire to form a point.Typically, the steel pin is then heat-treated, as by austempering whichproduces a ductile core in combination with surface decarburization, andthen plated with zinc, as by electrogalvanizing. Various additionalcoatings may also be applied to further improve corrosion resistance.

Commonly, the point is formed either by swaging the wire end or by pinchpointing, which refers to forging the wire end between two matched dies.Each point-forming process, as practiced heretofore, has its ownshortcomings.

Swaging is a slower process. Swaging tends to form a protuberance at thepoint. The protuberance tends to bend over, to deflect the steel pin,and to increase resistance to penetration, particularly as the steel pinis initially driven against a steel surface, whereby it may be undulydifficult to maintain perpendicularity of the steel pin relative to thesteel surface.

Pinch pointing is a faster process. Pinch pointing tends to form a cleftwhere the matched dies come together at the tip. Because of its strikingappearance under high magnification (for example, 60×magnification) thecleft that is formed is known as a "fish mouth" to persons involved withthe manufacture of steel pins.

In addition to resulting in a tip having either a protuberance or a"fish mouth", both swaging and pinch pointing processes make itdifficult to produce a smooth transition, which is required, where thepointed end of the steel pin meets the cylindrical shank of the steelpin.

Generally, a "fish mouth" cleft does not seem to unduly interfere withthe driving of a steel pin having such a cleft into a concrete ormasonry substrate by means of a powder-actuated tool, even if the steelpin must be initially driven through a thin-walled steel workpiece.However, such a cleft tends to increase resistance to penetration tosuch a high level that a steel pin having such a cleft cannot beeffectively driven by means of a low velocity powder-actuated tool so asto deeply penetrate a steel substrate. Although a larger powder chargeaids penetration of a steel pin into a steel substrate, such penetrationis not always successful even if such a charge is employed.

When a low velocity tool is employed, penetration of a steel pin, havingsuch a cleft, into a steel substrate tends to be arrested before allenergy from the powder charge that has been employed has been spent,whereupon the steel pin may break along its shank. It may be similarlydifficult to drive a steel pin, having such a cleft, through athick-walled steel workpiece by means of a powder-actuated tool.

Other alternative mechanical processes for forming a point on such a pininclude turn pointing and roll pointing. These processes leaveundesirble flaws, such as grooves in the point, or a sharp transitionbetween the point and the shank. It is believed that in every pin knownto the prior art, there is some section that has a gross surfaceimperfection deviating from the desired ogive shape.

Heretofore, it has been known to remove slight imperfections and smallburrs from such steel pins by tumbling the steel pins upon themselves,with or without media. As practiced heretofore, tumbling only is notentirely satisfactory, as tumbling tends to distort the clefts orprotuberances on the points of the tumbled pins. Because of thedistorted points, it can be more difficult to maintain perpendicularityof such pins relative to the steel substrates, and resistance topenetration of such pins into the steel substrates tends to also beincreased.

The purpose of tumbling practiced heretofore was to remove flash orupstanding thin-walled protuberances on the steel pins, a processcommonly known as deburring. The purpose was not to remove steel frommost of the surface of the tip of the pin.

TERMS USED HEREIN

References are made hereinafter to an ogive, which is the curved ortapered front portion of a projectile having a cylindrical body, orequivalently, of a steel pin having a cylindrical shank which has apredetermined shank diameter. An ogive is generated by a circular arc ora straight taper, arc or taper is rotated 360° about a central axis. Atangent or true ogive is generated by a circular arc tangent to thegenerator of the cylindrical surface of the cylindrical body, orequivalently, of the cylindrical shank. As generated by a circular arc,a tangent or true ogive has a radius which is the radius of the circulararc. A secant ogive is generated by a circular arc not tangent to, butintersecting at a small angle, the cylindrical surface thereof. Aconical ogive is generated by a straight taper intersecting thecylindrical surface thereof.

References are made hereinafter to a roughness-height index value, whichis a number that equals the arithmetical average deviation of minutesurface irregularities from a hypothetical perfect surface, as expressedeither in microinches (μin) or micrometers (μm). Surface-texturemeasurements expressed as roughness-height index values and relatedtopics are explained in Broadston, "Surface-Texture Designation,Production, and Control", which is a chapter in Baumeister et al.,Marks' Standard Handbook for Mechanical Engineers, Eighth Edition,McGraw-Hill Book Company, New York (1978) at pages 13-73 et seq.

As explained in Broadston, supra, flaws in a surface are not consideredin surface-texture measurements. Accordingly, references made herein toother surface imperfections refer to clefts, protuberances, and otherflaws that are not considered in surface-texture measurements, whichflaws include but are not limited to those flaws created by mechanicalpoint-forming processes.

Also, tip radius is defined as the radius at the very tip of the pin.

SUMMARY OF THE INVENTION

This invention has resulted from efforts to reduce resistance topenetration of a steel pin into a steel substrate, particularly a steelpin having a forged point having a "fish mouth" cleft, as describedabove.

This invention provides a steel pin having a substantially sharp point,which is reshaped so as to provide substantially true pointconcentricity, so as to reduce surface-texture irregularities, and toeliminate other surface imperfections apparent under high magnification.This invention also provides a method for the manufacture of the steelpin.

Broadly, the substantially sharp point has surface-textureirregularities with a roughness-height index not greater thanapproximately 30 microinches (approximately 0.76 micrometers) andappears to be substantially free of other surface imperfections whenviewed under high magnification, specifically when viewed under60×magnification. Preferably, for some applications, the substantiallysharp point has surface-texture irregularities with a roughness-heightindex value in a range from approximately 10 microinches (approximately0.25 micrometers) to approximately 15 microinches (approximately 0.38micrometers).

Desirably, the substantially sharp point conforms substantially to anogive except that the substantially sharp point has a substantiallyspherical tip. Desirably, the substantially spherical tip has a radiusin a range from approximately 0.02 inch (approximately 5 millimeters) toapproximately 0.03 inch (approximately 7.5 millimeters).

Preferably, the steel pin has a substantially cylindrical shank joinedto the substantially sharp point at a transition having a substantiallysmooth, continuously curved surface. In one contemplated embodiment, thesubstantially cylindrical shank is knurled near the transition, althoughit is not necessary for the substantially cylindrical shank to be soknurled.

From efforts to optimize the tradeoff between ease of penetration andholding power, it seems to be particularly preferable for thesubstantially sharp point to conform substantially to a tangent ogive,which has an ogive radius approximately ten times the shank diameter andan ogive length approximately twice the shank diameter, except that thesubstantially sharp point has a substantially spherical tips which has aradius approximately 0.1 times the shank diameter, particularly but notexclusively if the substantially sharp point has surface-textureirregularities with a roughness-height index in a range fromapproximately 15 microinches (approximately 0.38 micrometers) toapproximately 30 microinches (approximately 0.76 micrometers). The ogivelength includes the tip radius.

When a steel pin is made by the method provided by this invention, alength of steel wire is deformed so as to form a steel pin with asubstantially cylindrical shank, and with a substantially sharp pointwhich extends from one end of the substantially cylindrical shank andwhich may be made by one of the common mechanical pointing processes.The substantially sharp point is reshaped so that the substantiallysharp point has substantially true concentricity, so thatsurface-texture irregularities on the substantially sharp point have aroughness-height index value not greater than approximately 30microinches, and so that the substantially sharp point appears to besubstantially free of other surface imperfections when viewed under60×magnification. Such imperfections include those caused or left by thecommon mechanical pointing processes.

Preferably, the substantially sharp point is reshaped so thatsurface-texture irregularities on the substantially sharp point have aroughness-height index value in the range from approximately 10microinches (approximately 0.25 micrometers) to approximately 30microinches (approximately 0.76 micrometers) whereby a smooth transitionfrom the substantially sharp point to the substantially cylindricalshank is achieved. Desirably, the substantially sharp point is reshapedso as to have a substantially spherical tip and so as to conformsubstantially to an ogive except for the substantially spherical tip.Desirably, the substantially sharp point is reshaped so that thesubstantially spherical tip has a radius in the range from approximately0.02 inch (approximately 5 millimeters) to approximately 0.03 inch(approximately 7.5 millimeters).

Preferably, the substantially pointed end is reshaped by barrelfinishing the steel pin in finishing media. Another term for barrelfinishing, as employed for purposes of this invention, is tumblepointing. Alternatively, the substantially sharp point is reshaped byabrasively finishing the steel pin in a cylindrical disc machine inwhich a abrasive-coated disc is rotated so as to throw the steel pinrepeatedly against abrasive-coated sidewalls.

Tumbling or deburring, as practiced in the prior art, was not intendedto change the tip radius or the overall shape of a pin point. Accordingto this invention, however, the substantially sharp point is reshaped soas to have a substantially spherical tip which desirably has a radius inthe range noted above, as well as a smooth surface finish, smoothtransitions, and freedom from gross irregularities.

Preferably, deforming the length of steel wire includes forging one endof the length of steel wire so as to cause the forged end to become thesubstantially sharp point of the steel pin. Alternatively, deforming thelength of steel wire includes swaging, turn pointing, or roll pointingone end of the length of steel wire so as to cause the swaged end tobecome the substantially sharp point of the steel pin.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features, and advantages of this invention willbecome evident from the following description of a preferred mode forcarrying out this invention with reference to the accompanying drawingsin which like reference characters designate like or corresponding partsthroughout the several views, and wherein:

FIG. 1 is an elevational view of a steel pin embodying this invention,in a larger size, with a head, a shank having a knurled portion, and asubstantially sharp point.

FIG. 2 is an elevational view of a steel pin embodying this invention,in a smaller size, with a head, a shank that is not knurled, and asubstantially sharp point.

FIG. 3 is a flow chart of preferred major steps in the manufacture ofthe steel pin shown in FIG. 1. Preferred major steps in the manufactureof the steel pin shown in FIG. 2 are similar except that the knurlingstep is omitted.

FIG. 4 is a microphotograph (at 60×magnification) of a substantiallysharp point formed on a steel pin by a pinch pointing process after thesubstantially sharp point has been reshaped by barrel finishing infinishing media for a prescribed period of time for the purposes of thisinvention.

FIG. 5 is a microphotograph (at 60×magnification) of a substantiallysharp point formed on a steel pin by a pinch pointing process before thesubstantially sharp point is reshaped for the purposes of thisinvention. A pronounced "fish mouth" cleft is visible. FIG. 5exemplifies the prior art.

FIG. 6 is a microphotograph (at 60×magnification) of a substantiallysharp point formed on a steel pin by a pinch pointing process after thesubstantially sharp point has been reshaped by barrel finishing infinishing media for 28 hours for the purposes of this invention.

FIG. 7 is a microphotograph (at 60×magnification) of a substantiallysharp point formed on a steel pin by a swaging process before thesubstantially sharp point is reshaped for the purposes of thisinvention. A small protuberance at the substantially sharp point isvisible. FIG. 7 exemplifies the prior art.

FIG. 8 is a microphotograph (at 100×magnification) of a cross-sectionthrough the substantially pointed end of a steel pin and through a steelplate after the steel pin has been driven into the steel plate. Thesubstantially pointed end was formed by a pinch-pointing process and thesteel pin was reshaped as described below. Geometric shapes in FIG. 8are artifacts due to hardness tests.

FIG. 9 is a microphotograph (at 100× magnification) of a cross-sectionthrough the substantially pointed end of a steel pin and through a steelplate after the steel pin has been driven into the steel plate. Thesubstantially pointed end was formed by a swaging process and was notreshaped as described below. Geometric shapes in FIG. 9 are artifactsdue to hardness tests. FIG. 9 exemplifies the prior art.

FIG. 10 is a microphotograph (at 50×magnification) of a cross-sectionthrough the substantially cylindrical shank of a steel pin and through asteel plate after the steel pin has been driven into the steel plate.The steel pin, which has a substantially pointed end formed by apinch-pointing process, was reshaped as described below.

FIG. 11 is a microphotograph (at 50×magnification) of a cross-sectionthrough the substantially cylindrical shank of a steel pin and through asteel plate after the steel pin has been driven into the steel plate.The steel pin, which had a substantially pointed end formed by a swagingprocess, was not reshaped as described below. FIG. 11 exemplifies theprior art.

DETAILED DESCRIPTION OF PREFERRED MODE

As shown in FIG. 1, a steel pin 10 of a larger size constitutes a firstembodiment of this invention. The pin 10 has a relatively long,substantially cylindrical shank 12 having a given diameter, a head 14having a larger diameter than that of the shank 12 and formed at one endof the shank 12, and a substantially sharp point 16 formed at andextending from the other end of the shank 12. The point 16 conformssubstantially to an ogive, particularly to a secant or tangent ogive,except that the point 16 has a substantially spherical tip 18. The point16 is joined to the shank 12 at a transition 20. The shank 12 has aknurled portion 22 near the transition 20.

As shown in FIG. 2, a steel pin 10' of a smaller size constitutes asecond embodiment of this invention. The pin 10' has a relatively short,substantially cylindrical shank 12' having a given diameter, a head 14'having a larger diameter than that of the shank 12' and formed at oneend of the shank 12', and a substantially sharp point 16' formed at andextending from the other end of the shank 12'. The point 16' conformssubstantially to an ogive, particularly to a secant ogive, except thatthe point 16' has a substantially spherical tip 18'. The point 16' isjoined to the shank 12' at a transition 20'. The shank 12' does not havea knurled portion. The length of the shank 12' depends upon what is tobe fastened to the substrate.

Although the points 16, 16', conform substantially to a secant ogive,this invention may also be embodied in a steel pin having asubstantially sharp point conforming substantially to a tangent ogive.

The substantially sharp point of each one of the steel pins 10, 10' hassurface-texture irregularities with a roughness-height index value inthe range from approximately 10 microinches (approximately 0.25micrometers) to approximately 30 microinches (approximately 0.76micrometers). Further, the substantially sharp point of each one of thesteel pins 10, 10' appears to be substantially free of other surfaceimperfections when viewed under high magnification, specifically whenviewed under 60× magnification.

The substantially sharp point of each one of the steel pins 10, 10' hassubstantially true concentricity. The substantially spherical tip of thesubstantially sharp point of each one of the steel pins 10, 10' has aradius in the range from approximately 0.015 inch (approximately 3.75millimeters) to approximately 0.03 inch (approximately 7.5 millimeters).Also, on each one of the steel pins 10, 10', the transition between thesubstantially sharp point and the substantially cylindrical shank has asubstantially smooth, continuously curved surface. In each one of theillustrated embodiments, except for the substantially spherical tip, thesubstantially sharp point conforms substantially to a secant or tangentogive.

Having a substantially sharp point that has substantially trueconcentricity and a roughness-height index value not greater thanapproximately 30 microinches (approximately 0.76 micrometers) and thatappears to be substantially free of other surface imperfections whenviewed under high magnification, specifically when viewed under 60×magnification, are characteristics which distinguish each one of thesteel pins 10, 10' from steel pins sold and used previously. Having apoint that is free from gross irregularities because substantially alltraces of mechanical intersections have been removed is anothercharacteristic which distinguishes each one of the steel pins 10, 10'from steel pins sold and used previously. Having a point that conformssubstantially to an ogive except that the point has a substantiallyspherical tip is another characteristic which distinguishes each one ofthe steel pins 10, 10' from steel pins sold and used previously.

A steel pin having these characteristics offers significant advantagesover a steel pin lacking these characteristics. Because the point of asteel pin having these characteristics has substantially trueconcentricity, the point does not interfere with maintainingperpendicularity between the steel pin and a steel substrate. Outwardflow of the steel that is displaced as a steel pin having thesecharacteristics penetrates a steel substrate tends to be uniformlyconcentric, whereby initial frictional forces imparted to the steel pinand to the steel substrate as the steel pin begins to penetrate thesteel substrate are minimized.

Preferably, as explained below, a steel pin having these characteristicsis made so that surface-texture irregularities on its shank are similarto surface-texture irregularities on its point. Advantageously,therefore, resistance of the steel pin to withdrawal from the steelsubstrate is maximized. Because of the lack of gross irregularities onthe steel pin and because of the smooth surface of the steel pin, thereis more surface contact between the steel pin and the steel substrate.

Preferred major steps in the manufacture of the steel pin 10 are chartedin FIG. 3. Preferred major steps in the manufacture of the steel pin 10'are similar except that the knurling step described below is omitted.

Initially, in the manufacture of a steel pin, a steel wire is drawn froman initial diameter to a desired diameter. Conventional equipment isemployed in this step.

Thereupon, a length of wire is cut from the drawn wire, the head isformed on one end of the cut length, of wire and the head is stampedwith a manufacturer's mark. Conventional equipment is employed in thesesteps.

Thereupon, conventional pinch pointing equipment is employed to form thepoint on the other end of the same of wire length which, between thehead and the point, becomes the shank of the steel pin. Thus, asexemplified in the microphotograph that is FIG. 5, the point has apronounced "fish mouth" cleft.

Presently, it is preferred to employ a Hartford High Speed Point Former(Model 5-700) which is available commercially from The Hartford SpecialMachinery Co. of Simsbury, Conn., to form the point with a metal removalprocess.

Knurlinq refers to forming a pattern of depressions, or raised areas, onthe shank of the fastener for the primary purpose of increasing theholding power of the fastener.

If the shank of the steel pin is to have a knurled portion near thetransition between the shank and the point, conventional equipment isemployed to knurl the shank portion. As shown in FIG. 3, this knurlingstep is performed between the point-forming step and the next step.Alternatively, this knurling step is perfromed between the wire-cutting,head-forming, and head-stamping steps and the point-forming step. Thisknurling step is employed in the manufacture of the steel pin 10 but isomitted in the manufacture of the steel pin 10'.

The next step is a degreasing step, in which conventional solvents areemployed in conventional equipment to degrease the steel pin as formedin the prior steps.

After the steel pin has been degreased, the steel pin is reshaped bybarrel finishing or tumble pointing the steel pin in finishing mediaover an extended period, of time whereby the steel pin is provided withthe characteristics which distinguish the steel pins 10, 10' from steelpins known and used previously. The barrel finishing or tumble pointingstep removes substantilly all traces of mechanical intersections thatwere left on the steel pin after the point was formed. Barrel finishingin finishing media is also known as media finishing.

Conventional finishing media may be suitably used, such as CeratechCeramic Media (5/8"×1/4"). Conventional barrel finishing or mediafinishing equipment may be suitably employed, along with a magneticseparator with a demagnetizer, a spin dryer, and a wire spin basket.Alternatively, vibratory finishing equipment with appropriate media mayalso be used.

In successive steps after the steel pin has been barrel finished infinishing media for the extended period, of time the steel pin is heattreated by austempering which produces a ductile core in combinationwith surface decarburization, plated with zinc by electrogalvanizing,coated with a protective chromate, and packaged.

The extended period, of time possibly approaching 100 hours, duringwhich the steel pin must be barrel finished in finishing media toprovide the steel pin with the characteristics noted above, isdetermined empirically with due regard to the finishing media that areemployed and the finishing equipment that is employed.

Alternatively, the substantially sharp point is reshaped by abrasivelyfinishing the steel pin in a is cylindrical disc machine in which anabrasive-coated disc is rotated so as to throw the steel pin repeatedlyagainst abrasive-coated sidewalls. Such a cylindrical disc machine,which is thought to be suitable, is available commercially from AACEngineered Systems Inc. of Cinnaminson, N.J. Because such a cylindricaldisc machine is more agressive, as compared to barrel finishing, fewerhours are required for metal removal.

Alternatively, the knurling step may follow rather than precede thereshaping step which involves barrel finishing, tumble pointing, orabrasively finishing, as described above. It is preferable, in someinstances, for the knurling step to follow the reshaping step.

It is informative to compare the microphotographs that comprise FIGS. 4,5, and 6. FIG. 4 illustrates the substantially pointed end provided on asteel pin by pinch pointing, after barrel finishing of the steel pin infinishing media for 40 hours, whereby the substantially pointed end hasno apparent "fish mouth" cleft.

FIG. 5 illustrates the substantially pointed end provided on a steel pinby pinch pointing, before barrel finishing of the steel pin has begun,the substantially pointed end having a very pronounced "fish mouth"cleft. FIG. 6 illustrates the substantially pointed end provided on asteel pin by pinch pointing, after barrel finishing of the steel pin infinishing media for 28 hours, whereby the "fish mouth" cleft appears tobe substantially reduced but not entirely eradicated.

As seen in FIG. 5, the point tip radius of a prior art pinch-pointed pinis difficult to ascertain due to the "fish Mouth" cleft. The point tipradius of a pin substantially similar to this pin was determined, asnoted in Table I, by looking at the pin from the side so that the "fishmouth" cleft was not seen. The tip radius was measured on one of the twosides of the "fish mouth" cleft. As shown in FIG. 4, after barrelfinishing or tumble pointing for 40 hours, the tip radius can be takenat any rotational angle because the tip is truly concentric.

Moreover, as seen in Table I, the tip radius after barrel finishing ortumble pointing is larger than the tip radius of the originalpinch-pointed pin. It can be appreciated that this would also apply to apin point originally made by swaging.

Barrel finishing or tumble pointing of a steel pin reduces all of itsexterior dimensions, not merely its substantially pointed end, asexemplified by the following data obtained from three specimen pinsreshaped as described herein. The following data also shows, fromshortening of various dimensions, that barrel finishing or tumblepointing not only removes upstanding flash or protuberances but alsoremoves metal from the steel pin in its entirety.

                                      TABLE I    __________________________________________________________________________                     After                          After                Before                     Rehaping                          Reahaping                               Change (%)                                     Change (%)    Specimen          Dimension                Reshaping                     28 Hours                          40 Hours                               28 Hours                                     40 Hours    __________________________________________________________________________    Specimen A          Knurl 0.154 inch                     0.150 inch                          knurl not                                2.6%          Diameter        measured          Shank 0.615 inch                     0.592 inch                          0.575 inch                                3.7%  6.5%          Length          Head  0.298 inch                     0.297 inch                          0.295 inch                                0.3%  1%          Diameter          Ogive 0.237 inch                     0.320 inch                          0.212 inch                                7%    11%          Length          Point Tip                0.010 inch                     0.018 inch                          0.022 inch                               180%  220%          Radius          Fish Mouth                0.009 inch                     nil  nil          Shank 0.150 inch                     0.150 inch                          0.146 inch                               nil    2.6%          Diamater    Specimen D          Knurl 0.152 inch                     0.149 inch                          knurl not                                2%          Diameter        measured          Shank 0.739 inch                     0.718 inch                          0.696 inch                                2.9%  6%          Length          Head  0.298 inch                     0.297 inch                          0.295 inch                                0.3%  1%          Diameter          Ogive 0.231 inch                     0.209 inch                          0.191 inch                                9.5%  17%          Length          Point Tip                0.010 inch                     0.020 inch                          0.024 inch                               200%  240%          Radius          Fish Mouth                0.007 inch                     nil  nil          Shank 0.150 inch                     0.150 inch                          0.146 inch                               nil    2.6%          Diameter    Specimen C          Knurl 0.154 inch                     0.149 inch                          knurl not                                3%          Diameter        measured          Shank 0.866 inch                     0.832 inch                          0.814 inch                                4%    6%          Length          Head  0.298 inch                     0.297 inch                          0.294 inch                                0.3%  1%          Diameter          Ogive 0.228 inch                     0.199 inch                          0.190 inch                                13%   17%          Length          Point Tip                0.012 inch                     0.023 inch                          0.028 inch                               192%  233%          Radius          Fish Mouth                0.017 inch                     nil  nil          Shank 0.150 inch                     0.150 inch                          0.146 inch                               nil    2.6%          Diameter    __________________________________________________________________________

Tables II, III, and IV report hardness data taken at cross-sectionsafter steel pin D was driven into steel plate D, after steel pin E wasdriven into steel plate E, and after steel pin F was driven into steelplate F, respectively. Steel pin D, which embodied this invention, was asteel pin having a substantially pointed end formed by a pinch-pointingprocess and reshaped as described above. Steel pins E and F, which didnot embody this invention, were commercially available pins havingsubstantially pointed ends formed by a swaging process but not reshapedas described above.

If there is a phase change from martensite to ferrite near the surfaceof a steel pin, as a result of high frictional heating when the steelpin is driven into a steel plate, the surface hardness of the steel pinand its shear strength near its surface are markedly reduced. In view ofthe available data including the data in Tables II, III, and IV, it hasbeen concluded that there is less frictional heating and less resultantdeterioration in pin surface hardness when a steel pin embodying thisinvention is driven into a steel plate.

                  TABLE II    ______________________________________                                       Hardness                                       Converted to            Core or Depth from                         Hardness Measured on                                       Rockwell    Specimen            Surface      Knoop Scale   Scale Noted    ______________________________________    Steel Pin D            Care         635.4         59 C            Care         642.1         59 C            Care         652.4         60 C            0.040 inch   612.1         58 C            0.020 inch   481.8         50 C            0.010 inch   422.4         45 c            0.005 inch   390.1         42 C            0.002 inch   400.8         43 C    Steel Plate D            Core         167.3         86 B            Core         169.1         86 B            Core         161.2         84 B            0.010 inch   201.7         93 B            0.040 inch   214.2         96 B            0.020 inch   256.3         26 C            0.010 inch   257.1         26 C            0.005 inch   269.5         28 C            0.002 inch   237.0         36 C    ______________________________________

                  TABLE III    ______________________________________                                       Hardness                                       Converted to            Core or Depth from                         Hardness Measured on                                       Rockwell    Specimen            Surface      Knoop Scale   Scale Noted    ______________________________________    Steel Pin E            Core         642.1          57 C    Prior Art            Core         608.0          56 C            Core         603.4          55 C            0.040 inch   517.0          50 C            0.020 inch   419.7          43 C            0.010 inch   264.6          25 C            0.005 inch   185.5          90 B            0.002 inch   Hardness not measured                         due to distortion    Steel Plate E            Core         136.9          75 B    Prior Art            Core         147.1          79 B            Core         148.9          80 B            0.060 inch   231.0          99 B            0.040 inch   229.6          98 B            0.020 inch   238.1         100 B            0.010 inch   195.9          92 B            0.005 inch   179.1          89 B            0.002 inch   118.0 (?)      67 B    ______________________________________

                  TABLE IV    ______________________________________                                       Hardness                                       Converted to            Core or Depth from                         Hardness Measured on                                       Rockwell    Specimen            Surface      Knoop Scale   Scale Noted    ______________________________________    Steel Pin F            Core         592.8         55 C    Prior Art            Core         581.0         54 C            Core         606.5         56 C            0.040 inch   597.3         55 C            0.020 inch   550.2         52 C            0.010 inch   469.3         47 C            0.005 inch   275.6         26 C            0.002 inch   208.1         95 B    Steel Plate F            Core         150.5         80 B    Prior Art            Core         153.4         81 B            Core         160.3         83 B            0.060 inch   198.5         93 B            0.040 inch   223.9         97 B            0.020 lnch   252.9         23 C            0.010 inch   272.3         26 C            0.005 inch   265.0         25 C            0.002 inch   269.1         26 C    ______________________________________

Hardness data in Tables II, III, and IV also indicates that ferrite isnot formed from martensite near the surface of a steel pin made inaccordance with this invention when driven into a steel plate but thatferrite is formed from martensite near the surface of a steel pin madein accordance with the prior art and driven into a steel plate. InTables II, III, when IV, higher hardness values (for example, Rockwell42 C to Rockwell 60 C) are indicative of martensite being present,whereas lower hardness values (for example, Rockwell 25 C, Rockwell 26C, Rockwell 90 B, and Rockwell 95 B) are indicative of ferrite beingpresent.

Further evidence that there is less frictional heating during driving ofthe steel pin is available from microphotographic studies of changes ofmartensitic structures to ferritic structures when steel pins are driveninto steel plates. It is informative to compare FIGS. 8 and 9.

In FIG. 8, which illustrates a steel pin made in accordance with thisinvention and driven into a steel plate, the steel pin does not exhibita significant number of large grains which are indicative of ferritebeing present. In FIG. 9, which illustrates a steel pin made inaccordance with the prior art and driven into a steel plate, asignificant number of large grains appear which are indicative offerrite being present.

Because a steel pin that has been reshaped as described above hassurface-texture irregularities with a roughness-height index value notgreater than approximately 30 microinches and appears to besubstantially free of other surface imperfections when viewed under60×magnification, better surface-to-surface contact is achieved not onlyat the substantially pointed end but also along the substantiallycylindrical shank when the steel pin is driven into a steel plate, ascompared to steel pins known and used heretofore, which allows forbetter holding power of the steel pin. The fact that bettersurface-to-surface contact is achieved is illustrated by FIGS. 8 through11. A dark region leading to the upper edge of FIG. 8 is believed to bean entrapment of zinc that had been used to coat the steel pin.

When FIGS. 10 and 11 are compared, it is evident that the surface of thesteel pin shown in FIG. 10 and made in accordance with this inventionappears to have surface-to-surface contact over approximately 55% of thesurface area defined between the steel pin and the steel plate, and tobe substantially smooth, after the steel pin has been driven into asteel plate. A dark region shown between the pin surface and the platesurface, along the surface area defined therebetween, is believed to becomprise zinc that had been used to coat the steel pin. Furthermore, itis evident that the surface of the steel pin shown in FIG. 11 and madein accordance with the prior art appears to have surface-to-surfacecontact over approximately 55% of the surface area defined between thesteel pin and the steel plate, and to have large voids which arebelieved to have resulted from the irregular flow of the substrate steelof the steel plate over the pin surface, and which thus increase theresistance to the steel pin with respect to penetration of a steelsubstrate.

As described above, this invention alleviates two problems that havebeen attributed to surface irregularities on the pin point when a steelpin is driven into a steel plate. One such problem is that surfaceirregularities cause high frictional resistance which produces high heatand causes a phase change of martensite to ferrite near the surface.Ferrite is weaker than martensite in shear strength. The other problemis that surface irregularities produce surface voids which areattributable to the irregular flow of the substrate steel over the pinsurface.

Although this invention has been described primarily in connection witha steel pin having a forged point, as exemplified in FIG. 5, thisinvention may be alternatively used in connection with a steel pinhaving a swaged point, as exemplified in FIG. 7.

In summary, this invention comprises removing traces of mechanicalintersections that may be left on the substantially sharp point afterdeforming the length of steel wire by known mechanical processes. Thisinvention also comprises providing a steel pin so that surface-textureirregularities on the substantially sharp point of the steel pin have aroughness-height index value not greater than approximately 30microinches.

Various other modifications may be made without departing from the scopeand spirit of this invention. It is therefore to be understood thatwithin the scope of the appended claims, the present invention may bepracticed otherwise than as specifically described herein.

We claim:
 1. A method of manufacturing a steel pin which is adapted tobe driven into a substrate by means of a low-velocity tool, comprisingthe steps of:deforming a length of steel wire so as to form a steel pincomprising a substantially cylindrical shank havinq a predetermineddiametrical extent, and a substantially sharp point defined upon one endof said substantially cylindrical shank; and reshaping saidsubstantially sharp point so that said substantially sharp pointed endhas substantially true concentricity, so that surface-textureirregularities upon said substantially share pointed end have aroughness-height index value not greater than approximately 30microinches, so that said substantially sharp pointed end issubstantially free of surface imperfections when viewed under 60×magnification, and so that said substantially share pointed end has aconfiguration that conforms substantially to that of an ogive having anogive radius which is approximately ten times said diametrical extent ofsaid substantially cylindrical shank such that penetration of said steelpin into a substrate, as driven by a low-velocity tool, is facilitated.2. The method of claim 1 wherein the substantially sharp point isreshaped so as to have a substantially spherical tip and so as toconform substantially to an ogive except for the substantially sphericaltip.
 3. The method of claim 2 wherein the substantially sharp point isreshaped so that the substantially spherical tip has a radius in a rangefrom approximately 0.015 inch to about 0.03 inch.
 4. The method of claim1 wherein the substantially sharp point is reshaped by barrel finishingthe steel pin in a finishing medium.
 5. The method of claim 1 whereindeforming the length of steel wire includes forging one end of thelength of steel wire so as to cause the forged end to become thesubstantially sharp point of the steel pin.
 6. The method of claim 1wherein deforming the length of steel wire includes swaging one end ofthe length of steel wire so as to cause the swaged end to become thesubstantially sharp point of the steel.
 7. The method of claim 2,wherein:said substantially sharp point is reshaped so that saidsubstantially spherical tip has a radius which is approximately 0.1times said predetermined shank diameter.
 8. The method as set forth inclaim 1, wherein:said substantially sharp point is reshaped so that saidsurface-texture irregularities upon said substantially sharp pointed endof said steel pin have a roughness-height index value which is withinthe range of from approximately 15 microinches to approximately 30microinches.
 9. A method of manufacturing a steel pin which is adaptedto be driven into a substrate by means of a low-velocity tool,comprising the steps of:deforming a length of steel wire so as to form asteel pin that comprises a substantially cylindrical shank having apredetermined shank diameters, and a substantially sharp point definedupon one end of said substantially cylindrical shank; and reshaping saidsubstantially sharp point so that said substantially sharp pointed endof said steel pin has a configuration that conforms substantially tothat of an ogive having an ogive radius which is approximately ten timessaid predetermined diameter of said substantially cylindrical shank andwith an ogive length of approximately twice said predetermined diameterof said substantially cylindrical shank such that penetration of saidsteel pin into a substrate, as driven by a low-velocity tool, isfacilitated.
 10. The method of claim 9 wherein the substantially sharppoint is reshaped, so as to have a substantially spherical tip.
 11. Themethod of claim 10, wherein:said substantially sharp point is reshapedso that said substantially spherical tip has a radius which isapproximately 0.1 times said predetermined shank diameter.
 12. Themethod as set forth in claim 10, wherein:said substantially sharp pointis reshaped so that said substantially spherical tip has a radius whichis within the range from approximately 0.015 inch to approximately 0.03inch.
 13. A method of manufacturing a steel pin which is adapted to bedriven into a substrate by means of a low-velocity tool, comprising thesteps of:deforming a length of steel wire so as to form a steel pin thatcomprises a substantially cylindrical shank having a predetermined shankdiameter, and a substantially sharp point defined upon one end of saidsubstantially cylindrical shank; and reshaping said substantially sharppoint so that said substantially sharp pointed end of said steel pin hasa configuration that conforms substantially to that of an ogive havingan ogive radius which is approximately ten times said predetermineddiameter of said substantially cylindrical shank such that penetrationof said steel pin into a substrate, as driven by a low-velocity tool, isfacilitated.
 14. The method as set forth in claim 13, wherein:saidsubstantially sharp point is reshaped so as to have a substantiallyspherical tip.
 15. The method as set forth in claim 14, wherein:saidsubstantially sharp point is reshaped so that said substantiallyspherical tip has a radius which is approximately 0.1 times saidpredetermined shank diameter.
 16. The method as set forth in claim 14,wherein:said substantially sharp point is reshaped so that saidsubstantially spherical tip has a radius which is within the range fromapproximately 0.015 inch to approximately 0.03 inch.
 17. A method ofmanufacturing a steel pin which is adapted to be driven into a substrateby means of a low-velocity tool, comprising the steps of:deforming alength of steel wire so as to form a steel pin that comprises asubstantially cylindrical shank portion having a predetermined shankdiameter, a substantially sharp point defined upon one end of saidsubstantially cylindrical shank portion such that said substantiallysharp point has a configuration that conforms substantially to that ofan ogive having an ogive radius which is approximately ten times saidpredetermined diameter of said substantially cylindrical shank portion,and a transition region defined between said substantially cylindricalshank portion of said steel pin and said substantially sharp pointed endof said steel pin; and refinishing said substantially sharp pointedogive end of said steel pin, said transition region of said steel pin,and said substantially cylindrical shank portion of said steel pin so asto form surface finish means, upon said substantially sharp pointedogive end of said steel pin, said transition region of said steel pin,and said substantially cylindrical shank portion of said steel pin, forestablishing surface-to-surface contact with interior sidewall portionsof a bore formed within a substrate when said steel pin is driven into asubstrate by a low-velocity tool such that penetration into a substrate,holding power within a substrate, and withdrawal resistance out from asubstrate, of said steel pin, including said substantially sharp pointedogive end of said steel pin, said transition region of said steel pin,and said substantially cylindrical shank portion of said steel pin, ismaximized.
 18. The method as set forth in claim 17, wherein:saidsubstantially sharp point is reshaped so as to have a substantiallyspherical tip.
 19. The method as set forth in claim 18, wherein:saidsubstantially sharp point is reshaped so that said substantiallyspherical tip has a radius which is approximately 0.1 times saidpredetermined shank diameter.
 20. The method as set forth in claim 18,wherein:said substantially sharp point is reshaped so that saidsubstantially spherical tip has a radius which is within the range fromapproximately 0.015 inch to approximately 0.03 inch.